1. Field of the Invention
The present invention relates to low temperature fired ceramics especially useful in the manufacture of electronic components or parts and further useful in other various application, such as heat-resistance industrial articles, tablewares, kitchen utensiles and decorative articles.
2. Description of the Prior Art
With the increasing trend toward high-speed computers and high-frequency devices or equipments, substrates having a low dielectric constant have been increasingly demanded in place of alumina substrates in current use because the conventional alumina substrates have a large dielectric constant (.epsilon.=10) which may cause the delay of signals. Further, the conventional alumina substrates are necessary to be fired at high temperatures and, thus, conductive materials used on the substrates are limited only to high melting point metals, such as Mo or W which may delay signals due to their relatively high electrical resistance.
Under such circumstances, certain ceramic compositions firable at low temperatures of 1100.degree. C. or less have been put into practical use to provide fired ceramics having a low dielectric constant and a thermal expansion coefficient near that of silicon so as to minimize the stress caused due to the difference of thermal expansion between the substrate and large sized silicon chips in view of a LSI chip. Such low temperature ceramic compositions can be co-fired with Au, Ag, Ag-Pd or Cu and thereby allow the use of these low melting point metallic materials as conductor on the ceramics.
For example, the inventors have proposed low-temperature firable ceramic composition comprising CaO-Al.sub.2 O.sub.3 -SiO.sub.2 (-B.sub.2 O.sub.3) glass and alumina in our previous U.S. patent application, Ser. No. 716,722, filed Mar. 27, 1985, now Patent No. 4,621,066. This ceramic composition develops superior electrical and mechanical properties in the fired products and can be subjected to high speed firing. Since in the course of the firing process, the ceramic composition is partially crystallized, it exhibit a superior ability to prevent deformation of the patterns of conductors and resistors when firing or re-heating treatment.
However, since in the above materials developed by the inventors, an alumina content is limited to a maximum amount of 50%, they have still some problems in their mechanical strength. In order to improve their mechanical strength, it is necessary to increase the use of alumina, and in this invention even if an alumina percentage is increased, it is possible to obtain fully densified fired ceramics.